Still needs a few details- I am fabricating a cover that will go over the tank and make it look more pre -WWI, and plates to blend the engine mounting plate so it does not look so flat- but she hit 40 mph Saturday- with a 56 tooth sprocket- I have a 48 tooth....so far I have no interest in installing it.
H
HoughMade
Guest
Only if you want a 12+ pound weed wacker- this is more like a spruced up generator engine. 
ocscully
Member
Back when you started this thread you mentioned 40mph with a 56t rear sprocket. I have a couple of questions please. I'm currently trying to finalize a belt Drive train for my project using the Honda GXH50 engine and when I run the numbers thru the ratio calulator that jpilot posted here at MBc I get speeds that are off by a factor of 25% The numbers I'm using are as follows 4.2:1 reduction for gearbox so I enter a 10t and a 42t then for the final drive I enter 11t to 56t . The software comes up with a total reduction of approx 21:1 with a max speed of 28mph@7800rpm for a bike with 26in. wheels. What I'm trying to understand is the error or difference between the math provided by the calculator and your actual in the field results. The belt drivetrain I've currently worked out provides a total reduction of 17.6:1, 3.5:1 in the primary 20t to 70t, and 5.1:1 for the final 20t to 102t. The calculator indicates a max speed of 35mph@7800rpm for this set up but if I factor in the error above its way faster than I need to be going on a motorized bicycle. Any insights you might be able to provide would be greatly appreciated.
ocscully
H
HoughMade
Guest
OK- here we go....I'm a lawyer, not a a mathemetician, but I'm pretty sure my numbers add up.
The difference appears to be that you are assuming a gearbox reduction of 4.2:1- the Grubee gearbox for the 4 stroke does not have that ratio. Perhaps that is the ratio for the standard 2 stroke. I don't know.
[edit] I see that the Grubee website lists the gearbox reduction as 4.2:1- that is wrong and does not even match their own numbers. They also list the final ratio as 9.29:1 with a 11 tooth to 56 tooth sprocket. I listed it as 9.3:1. 11 to 56 tooth results in 5.09 (as below), meaning for a final drive of about 9.3:1, the gearbox must be 1.83:1- and this fits with my observation of my own gearbox[/edit]
The Grubee gearbox has a reduction of 1.83 to 1 internally. The output sprocket is an 11 tooth and the wheel is 56 tooth. Therefore, that reduction is 5.09:1. That is multiplied by the gearbox reduction of 1.83:1 to get a total reduction of about 9.3:1 from crankshaft to wheel.
A 2.125" 26 inch wheel actually has an outside diameter of about 26 inches. The circumference is about 81.7 inches or 6.8 feet. In one mile, the wheel will travel 5280 feet, so it goes around 776.5 times. Multiply that by 40, becouse I was speaking of traveling 40 miles in one hour- you get 31,058.8 revolutions per hour, or, divided by 60, 517.6 revolutions of the back wheel per minute.
So- the back wheel does 517.6 rpm at 40mph- to figure the engine rpm, we just multiply by the total reduction, 9.3, and we see the engine rpm is 4,814 rpm @ 40mph. this is well within the engine's rpm range of a maximum of 7800, no load.
To anticipate someone else's question, if the rated maximum rpm of the GXH50 is 7800 rpm, why can't we get a top speed of 64 mph? There is not enough horsepower to push my large behind, the wind and the bike to the engine's maximum no-load rpm (that's why its a "no load" rpm)
The difference appears to be that you are assuming a gearbox reduction of 4.2:1- the Grubee gearbox for the 4 stroke does not have that ratio. Perhaps that is the ratio for the standard 2 stroke. I don't know.
[edit] I see that the Grubee website lists the gearbox reduction as 4.2:1- that is wrong and does not even match their own numbers. They also list the final ratio as 9.29:1 with a 11 tooth to 56 tooth sprocket. I listed it as 9.3:1. 11 to 56 tooth results in 5.09 (as below), meaning for a final drive of about 9.3:1, the gearbox must be 1.83:1- and this fits with my observation of my own gearbox[/edit]
The Grubee gearbox has a reduction of 1.83 to 1 internally. The output sprocket is an 11 tooth and the wheel is 56 tooth. Therefore, that reduction is 5.09:1. That is multiplied by the gearbox reduction of 1.83:1 to get a total reduction of about 9.3:1 from crankshaft to wheel.
A 2.125" 26 inch wheel actually has an outside diameter of about 26 inches. The circumference is about 81.7 inches or 6.8 feet. In one mile, the wheel will travel 5280 feet, so it goes around 776.5 times. Multiply that by 40, becouse I was speaking of traveling 40 miles in one hour- you get 31,058.8 revolutions per hour, or, divided by 60, 517.6 revolutions of the back wheel per minute.
So- the back wheel does 517.6 rpm at 40mph- to figure the engine rpm, we just multiply by the total reduction, 9.3, and we see the engine rpm is 4,814 rpm @ 40mph. this is well within the engine's rpm range of a maximum of 7800, no load.
To anticipate someone else's question, if the rated maximum rpm of the GXH50 is 7800 rpm, why can't we get a top speed of 64 mph? There is not enough horsepower to push my large behind, the wind and the bike to the engine's maximum no-load rpm (that's why its a "no load" rpm)
Last edited by a moderator:
H
HoughMade
Guest
I see the Grubee site's error
The Grubee site linked above make a basic math error which accounts for why they list the gearbox ratio at 4.2:1. They did this: the knew the final ratio of 9.29:1 and they knew the reduction from sprocket to sprocket of 5.09:1. they somply substracted 5.09 from 9.29 to get 4.2. Here is the problem. when you gear something down twice, you do not add the ratio to determine final drive, you multiply. Therefore, what they should have done is take the final drive of 9.29 and divided by the 5.09. Had they done this, they would have come up with a gearbox ratio of 1.825:1...essentially the 1.83:1 I rounded to.
When you plug 10 teeth to 18.3 teeth and 11 teeth to 56 teeth into the calculator you used, then enter 4814 rpm, you will come out with a speed of 40mph.
The Grubee site linked above make a basic math error which accounts for why they list the gearbox ratio at 4.2:1. They did this: the knew the final ratio of 9.29:1 and they knew the reduction from sprocket to sprocket of 5.09:1. they somply substracted 5.09 from 9.29 to get 4.2. Here is the problem. when you gear something down twice, you do not add the ratio to determine final drive, you multiply. Therefore, what they should have done is take the final drive of 9.29 and divided by the 5.09. Had they done this, they would have come up with a gearbox ratio of 1.825:1...essentially the 1.83:1 I rounded to.
When you plug 10 teeth to 18.3 teeth and 11 teeth to 56 teeth into the calculator you used, then enter 4814 rpm, you will come out with a speed of 40mph.
Last edited by a moderator:
ocscully
Member
HoughMade,
Thank you for responding with your observations. I went to the GRUBEE web site and started counting gear teeth and running the numbers thru the calculator after reading your most recent posts to help me understand what is going on between the math and the actual experiences members of MBc are reporting. Your figures for the GRUBEE gearbox didn't add up in my mind, so I did some checking on my own and here is what I came up with. The primary driver on the clutch bell of the GRUBEE is 35t engaging a 54t/20t stepped gear in the middle, the smaller 20t in the middle engages a 48t gear which drives the gearbox output cog 11t sprocket. I calculate the gear box to have a reduction of 3.7:1, The final drive is as you stated 5.09:1 reduction for a total reduction of 18.85:1 for the GRUBEE install kit. This figure is in keeping with what seems to be the range of reduction from the various engine suppliers in the motored bike industry. Staton Inc. 18.75:1, GEBE 19:1 to 24.5:1 with 22.5:1 being their mid ratio, Happy Time suppliers seem to be in the just under 18:1 ratio with a 44t rear sprocket. None of these systems match up when you run the numbers/math versus actual reported top speeds. This inconsistency has created a quandry for me in making the right decisions for the Timing Belt drivetrain I'm attempting to put together for my GiantStone project. I spent some time today searching and reading various posts and threads here on MBc and still have not found an answer for the difference between the math and riding experience. I guess I'll just have to jump in and and hope for the best.
ocscully
Thank you for responding with your observations. I went to the GRUBEE web site and started counting gear teeth and running the numbers thru the calculator after reading your most recent posts to help me understand what is going on between the math and the actual experiences members of MBc are reporting. Your figures for the GRUBEE gearbox didn't add up in my mind, so I did some checking on my own and here is what I came up with. The primary driver on the clutch bell of the GRUBEE is 35t engaging a 54t/20t stepped gear in the middle, the smaller 20t in the middle engages a 48t gear which drives the gearbox output cog 11t sprocket. I calculate the gear box to have a reduction of 3.7:1, The final drive is as you stated 5.09:1 reduction for a total reduction of 18.85:1 for the GRUBEE install kit. This figure is in keeping with what seems to be the range of reduction from the various engine suppliers in the motored bike industry. Staton Inc. 18.75:1, GEBE 19:1 to 24.5:1 with 22.5:1 being their mid ratio, Happy Time suppliers seem to be in the just under 18:1 ratio with a 44t rear sprocket. None of these systems match up when you run the numbers/math versus actual reported top speeds. This inconsistency has created a quandry for me in making the right decisions for the Timing Belt drivetrain I'm attempting to put together for my GiantStone project. I spent some time today searching and reading various posts and threads here on MBc and still have not found an answer for the difference between the math and riding experience. I guess I'll just have to jump in and and hope for the best.
ocscully
Last edited:
H
HoughMade
Guest
Good work- I will look into it. I guess my speedometer could be off- that is certainly possible. I want to be accurate, and if I have not been, i want to correct. I may just have to break out the sharpie and count revolutions.
I
Irish John
Guest
Gear ratio
This is very interesting. I am going to see if I can calculate the top speed myself because I've just bough a 4-stroke kit and want to know what I can expect as a comfortable cruising speed. Not that I don't trust the calcs above - I'm sure they are right. Presumably the Honda GXH 50 and the Chinese Huangshen Rip-off have the same performance statistics - does anyone know what the max rpm of the Chinese 4-stroke is?
This is very interesting. I am going to see if I can calculate the top speed myself because I've just bough a 4-stroke kit and want to know what I can expect as a comfortable cruising speed. Not that I don't trust the calcs above - I'm sure they are right. Presumably the Honda GXH 50 and the Chinese Huangshen Rip-off have the same performance statistics - does anyone know what the max rpm of the Chinese 4-stroke is?
H
HoughMade
Guest
D
Dockspa1
Guest
That is classy Houghmade! Excellent job!
Love the white tires.
Doc
Love the white tires.
Doc
E
eltatertoto
Guest
lookin good!!!
Similar threads
- Article
- Locked
